Monitoring one of the tipping points of the AMOC

• Main Authors: Larsen, Karin Margretha H., Hansen, Bogi, Østerhus, Svein
• Format: Conference Object
• Language: English
• Published: Zenodo 2018
• Subjects: AMOC; Tipping point; Monitoring; Greenland-Scotland Ridge; Greenland; Nordic Seas
• Online Access: https://doi.org/10.5281/zenodo.1188871

Abstract The deep limb of the AMOC is fed by two main sources: a western source generated by deep convection in the Labrador/Irminger seas, and an eastern source originating in overflow of dense water from the Nordic Seas across the Greenland-Scotland Ridge, which is enhanced by water entrained after passing the ridge. These two sources behave very differently. The intensity of the western source varies dramatically from one year to another. Two decades of monitoring, in contrast, reveal that the overflow is remarkably stable. In the simple thermohaline paradigm, the generation and maintenance of overflow is linked to the properties of the compensating inflow of Atlantic water to the Nordic Seas, especially its salinity and hence its density after cooling. Watching how far this part of the AMOC is from a potential tipping point therefore involves observing the transport of mass and properties of the overflow and the inflow. Here, we focus on the densest of the overflow branches, the Faroe Bank Channel (FBC) overflow and the strongest of the Atlantic inflow branches, the Faroe Current (FC). During the last two decades, the volume transports of both these flows have remained stable with perhaps a weak increase, but the properties have changed. After the mid-1990s, both the temperature and the salinity of the FC increased. Similar trends have been observed for the FBC-overflow, although somewhat delayed and much reduced. Thus, the FBC-overflow has remained stable in density as well as volume transport. Since 2016, however, there has been a dramatic reduction in the salinity of the FC and hence the transport of salt into the generation area of the overflow water. Future monitoring of the Greenland-Scotland Ridge exchanges and its properties, thus, has a high priority, and emphasizes the need to continuously develop the monitoring systems and integrate them with remote sensing and new technology.